Method of shaper cutting gears



July 7, 1953 w. s. PRAT-:G 2,644,367

METHOD oF sHAPER CUTTING TEARS WALTER S. PR'A E G July 7, 1953 w. s. PRAEG 2,644,367

METHOD OF SHAPER CUTTING' GEARS Filed Jun 28, 1948 2 Sheets-Sheet 2 n ing and a specific tool. .is a continuation-impart of my prior copending Ycutter upon initiation of -terized further by cutting ,strokes in :ciprocation .between a cutter and work piece;

Patented July 7, 1953 UNITED STATES 'maar orticay 2,644,367 I METHOD 'OF SHAPER CUTTING GEARS Walter S. Praeg,

mesne assignments, t

Company, Springfield, Vt.,

Vermont Detroit, Mich., assigner, by

o The Fellows Gear Shaper a corporation of Application .I une 28, 1948, Serial No. 35,610

3 Claims.

, the invention is applicable to an ordinary shape-r operation or planing operation it finds its most advantageous expression in a Shaper operation characterized further by a method adapted to form tooth-like portions on a work piece such for example as straight or helical teeth on a cylindrical gear.

In the preferred form of the invention the cutting tool comprises three main portions; first, a

rigid support portion; second, a relativelymovable portion having cutting edges carried there- `by; and third, a flexible portion intermediate the other two portions and adapted to permit relative mov-ement between the cutting portions and the rigid support portion.

The invention includes a'machine for carrying out the `processa new method o-f metal work- The present application application Serial No. 683,650, filed July 15, 1946,

1 adapted to carry out the present invention;

and which has matured into Patent No. 2,604,016- y issued July 22, 1952, and is directed to the method. A cutting tool which may be employed is described in my co-pendingapplication No. 35,609,

filed June 28, 1948.`

It is an object of the present invention to provide a new method for carrying out a shaper operation in which cutting clearance is automatically provided by a relative movement of the the cutting stroke. It is a further object of the invention to providealternatively for substantially increased speed in the cutting operation or substantially greater accuracy of the finished product in the same time as employed by present day conventional shaping operations. It is a further object of the Vpresent invention' to provide for metal shapingcharacterized by the provision of a shaper cutter whose life may be substantially increased by reversing the shaper cutter; characterized further by theprovision of a cutter-,for cutting vhelical parts adapted to perform its cutting operation alternately on opposite sides of toothed members of a work piece; characterized further by the provision of a disc-like cutterhaving a rigid hub and rim interconnected by a flexible web; characa machine adapted to perform both directionsv of relative reof cutting employingra cutter having identical cutting edges at opposite fac-es thereof in which cutting clearance for the trailing face is provided by inclina'- tion of the cutter during vthe cutting stroke; and characterized finally by a method of cutting shoulder gears in which the cutter is inclined to a clearance position on a cutting stroke toward the shoulder and moves to a neutral clearance position on the return stroke.

Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings, wherein:

Figure i is a diagrammatic View of a machine Figure 2-is a fragmentary axial section showing the improved cutting tool assembly;

Figure 3 isa diagrammatic View illustrating the manner in which cutting clearance is provided;

Flgure 4 is a diagrammatic View illustrating the lateral displacement of cutting teeth relative to a helical work piece so as to provide for cuts alternately on opposite sides of the teeth;

.Figure 5 is a Ydiagrammatic View illustrating the application of the present invention to the cuttingof shoulder gears; and i 'Figure 6 is a fragmentary section illustrating a modified form of cutter.

Referring first to Figure '1, there is illustrated a i'nachinel tool comprising a base i0 having mounted thereon a work support il and a tool support i2. The machine is of the type com- 35'Nmonly referred to in the art as a gear shaper and is adapted to provide for relative cutting reciprocation between a cutter substantially in the form of a gear, and a gear blank. in practice the cutterlwhile being reciprocated axially is fed into thev gear blank to a predetermined depth while the cutter and gear blank are both slowly rotated; and thereafter, while relative vreciprocation` continues, both the rcutter and the gear blank are rotated slowly with the result that the vteeth of the cutter generate conjugate, teeth on the work piece. i

Y A. single motor t3 is provided which drives all of the parts, as Vwill now be described. The motor v E3 rotates a shaft lll through suitable driving connections such as a belt l5. The shaft ill has a crank i5 which-through a link il and a crosshead i3 is adapted to reciprocate a spindle I9 which carries the tool assembly 26. l A

The shaft ill carries a 'bevel gear 2l Vwhich drives a shaft 22 through the medium of a meshing bevel gear 23 and the shaft 22 has as its end a worm 2d which drives a worm wheel 25. The worm wheel 25 drives a pair of meshing gears 26 and 2i through the medium of bevel gears 28. The gear 21 has a shaft to which is secured a worm 30 meshing with a worm wheel 3i formed on the outer portion of a housing 3'2 which is mounted for rotation in bearings indicated at 33. The crosshead I8 previously referred to has a driving connection indicated generally at 35 for reciprocating the spindle le, the connection 35 permitting rotation of the spindle i9 relative thereto. The spindle IQ is provided with a cylindrical enlargement 3B which has teeth or splines thereon engageable in corresponding teeth or splines 39 formed on the interior of the housing 32. parent that rotation or" the housing 32 through the medium or its worm 3l will result in a corre spending rotation or" the spindle I9 and the tool assembly 2li.

1n the event that a gear carried by the work support l I is being cut which has straight teeth, the teeth or splines on the enlargement 38 and the corresponding teeth or splines 3&3 on the inn terior of the housing 32 will be straight, that is, parallel to the axis of the housing :32. If, however, the teeth cn the gear being cut are helical the teeth or splines on the enlargement '3S and the teeth or splines Si) on the interior of the housing 32 are helical. Accordingly, the cutter assembly will be provided with a slow continuous rotation through the medium of its worin gear 3| and in addition a relative oscillation about its axis will be provided due to the reciprocation of the enlargement 3S and the helical mating surfaces formed on t'he member -36 and the interior of the housing 32.

In order 'to provide for an accurately timed ro tation of the gear yblank relative to the slow timed rotation of the tool assembly 2Q, bevel gear ill is provided which meshes with a similar bevel gear carried 'by the shaft on which are mounted the gear "2i and the worin 3S. The bevel gear 4S is connected to across shaft 4l which extends to the work support and rotates ahousing 32 through the medium o'f bevel gears 453, 4, mating gears 45, e5 and '41,'wor1n 23B and worin gear es. vThe work supporting spindle 5'@l is mounted for rotation in Vbearings indicated at '5i and includes a chuck 52 for receiving the Ygear blank to be out.

It will be apparent that the machine structure 'thus 4far described does not provide any means for effecting a relieving motion of the tool relative tothe work piece on the back stroke as is now conventional. 'In other words, the machine is adapted to effect a cutting stroke in both direc= tions of relative reciprocation between the work piece and the tool assembly.

'In orderto effect cutting in both directions of reciprocation a cutter assembly as illustrated in deta'il'in 'Figure `2 is provided. in this yfigure the It will thus be apcutter spindle is indicated at it, which is shown v as provided with a threaded portion l on which kengage clamping nuts and 52. lBetween the clamping nuts 'Gil vand e2 are provided the cutter S3 and a pair of annular abutment 'members B. The cutter "G3 is provided with a central rigid hub vportionlili Whiche'n'gages over the spindle lil; an outer 'rigid annular rim portion E5, carrying cutting teeth or elements 6G; andan intermediate annular thin exible web el' which permits relative'm'overnent between the hu'b tfl and the rim 65.

The web 61 is designed such that it will permit ja relative rocking movement 'of the rim 55 about the center of the tool assembly C 'when the cutting portions e6 initially engage the work piece. At the same time, the web 6l is of suiiicient thickness such that it prevents any other relative movement between the hub 613 and the rim 55. It will be appreciated that when the cutting operation being performed is a gear cutting operation, that the rocking movement of the rim S5 is `about an axis which is perpendicular to the axis of the cutter assembly and perpendicular to the line joining the center of the cutter assembly and the center of the gear blank and which passes substantially centrally through the cutter assembly.

By wayofrexa'inple, very successful gear cutting operations have 'been performed where the dimensions of the cutter 63 are approximately as follows: The thickness of the hub 134 is .500 inch the thickness of the rim 6E is .484 inch, the thickness of the web 57 is .100 inch and the radial di= mension of the web between the hub Sli and the rim 65 is approximately 1.5 inches.

Depending upon the dimensions of the cutter parts, there may be incre or less flexing ci the rim 65 in addition to or in place of the rocking motion of the rim as a unit. Thus it may be possible to obtain sufficient tipping or inclining of the teeth 66 to provide cutting clearance with less spacing betw'een'the abutments G8 and rim t5. ln either case however the cutter supports the cuttingteeth against undesirable Alateral movement or moveu ment radially of the cutter. The rocking of Ythe teeth actually engaged in cutting is therefore about an axis which is perpendicular to the axis of the cutter and perpendicular to the line joining the centers of the gear blank and cutter, and located between the planes donned by the cutting edges of the cutter teeth, and between the axis of the cutter and the portion thereof engaged in cutting.

Rocking motion 'of the rim 65 of the cutter 63 is limited by :faces ill formed on the abutment members 68 and these faces are in the specic embodiment under discussion spaced from the adjacent faces of the rim E5 by .603 inch. It will be appreciated that the'fcregoing heures have been given merely to enable those skilled in the .art to understand a successful embodiment of the pres= ent invention vand are in no sense to lbe considered as limiting. As a matter-of fact, it is contenua plated that the thickness of 'the web 6l may be between .G75 and .1725 inch and the spacing between the faces lo of the abutment members S8 or 'cooperating faces of the rim 'S5 may be between .003 and .015 inch..

Attention is now directed to Figure 3, which is a diagrammatic showing on `an enlarged scale illustrating the manner in which cutting clearance is automatically provided. In this figure the rim 65 is illustrated in full lines in an intermediate position equally 'spaced from the abutment surfaces 70 of the annular members 58. The cuttingp'ortion 66 is provided with cutting edges at opposite ends thereof, the tips of the cutting nedges being indicated atten and 56h.

The prole `ofthe#cutting edges are videntical so `that if the Ycutter assembly were reciprocated A vevent that none .mate radial lines'it may be that no additional vadvantage of the vnow follow the trace 14 and the corner 66h will followthe trace 15. In other words, cutting clearance for the corner dicated by the dimension d is provided. It will of course be apparent that in the case of a cutter having cutting portions 66 in the form of gear teeth, thecutting clearance provided at the sides of the teeth will be a function of the angularity of thesesurfaces with radial planes. In other words, a portion of the cutter tooth surface which occupies a plane perpendicular to the radius kof the cutter will have a maximum amount of cutting clearance. In like manner, a portion of the cutter tooth occupying a truly radial plane would be provided with no clearance by this rocking motion. In practice, how-= ever, there are no radial surfaces provided so that some cutting clearance isr provided in back of every portion of each of the cutting edges bythe rocking motion of the rim-65. In` the of the cutting edges approxicutting clearance need Abe provided. However, in some cases it may be desirable to modify 'the sides of the teeth as by vhollow grinding so as to provide additional clearance directly in back of the cutting edge. In all cases, however, the cutting clearance for the trailing or inactive cutting edge will'result solely from inclination of the cutterlrelative to the path of relative reciprocation.

In the case of the specific cutter whose di= mensions were given above the tip of the `cutter tooth was provided withA a hollow `whose depth at its center midway between the cutting edges of the tip lwas .001 inch and the sides of the cutting teeth were provided with a hollow which amounted to vapproximately .002 inch midway between the cutting edges. y

It is desired to emphasize, however, that in many cases no additional clearance need be ground into the cutting teeth, with the result that an extremely inexpensive cutterY results, the side surfaces of the cutting teeth being ground so that each tooth is of uniform thickness'v throughout.

It is desired at this time to mention a prime present method of shaping. It is inherent in this type of shaping where it is used to shaper cut gear teeth that a major portion of the cutting action is done by the leading corners of the cutting teeth. In accorci-s ance with the present invention the cutter is reversible and sometime prior to dulling of the leading corners of the cutter teeth the cutter may be reversed so that the opposite corners of -its teeth will become the leading corners and thus subjected to the heaviest cutting strain.

It will be appreciated that cutting performed by this improved cutter may be vsubstantially twice as rapid as conventional cutting which takes place in one direction only and in which cutting stroke is followed by back-out of the tool and a return idle stroke. As a matter of fact, it is possible to reduce cutting time to somewhat less than half of that previously required for the reason that some time is involved lin the backing out of the tool from the work prior to the idle stroke and this of course is totally avoided in the present invention. Y

If instead of employing the cutter in a manner to reduce the cutting `time to a minimum, the rate of rotation is kept substantially equal to the relative rotation in single stroke cutting, it will be appreciated that the result will be to 66h in an amount inproduce a finished gear tooth of very substantially increased accuracy due to the fact that the number of cuts per unit area of surface have been doubled.

Referring now to Figure 4, there is illustrated a novel manner of cutting helical gear teeth which results from employing the cutter described herein in conjunction with helically formed teeth 80 thereon. In this figure aportion of the work gear is indicated at 8l and at 82 there is illustrated a tooth space in which the cutter tooth 8!) is operated. It will be appreciated that in this operation the Shaper is one in which the tool spindle i9 has an enlargement 38 which is provided with helical teeth or splines thereon for cooperation with similar teeth or splines 39 formed on the interior of the rotatable housing 32. In Figure 4 it may be assumed that the cutter tooth 80 is rst moved `downwardly along a path 83 which for clarity"` is developed into a straight line path and that dueto the feed between the tool and cutter the tooth Bil will engage metal at the sides of the tooth slot-82 formed in the blank 8|. Upon initial engagement ofthe toothy at and the upper surface of the gear blank 8l the cutter will rock about the axis previously described until .such

time as the rim of the cutter engages the abutment surface i0 thereabove. During this rocking motion of the rim of the cutter, an additional slight rotation of the cutter assembly will result from the continued downward movement of the hub portionthereof. This slight additional downward movement of the hub portion of the cutterresults in lateral displacement of the cutter tooth 0 to thek position indicated in dotted lines at 89a, which it will be observed is slightly offset with'respect to the tooth space 32. lContinued movement of the tooth 80 and the cutting stroke will therefore remove metal from the side of the tooth slot designated 82a and there will be clearance between the other side. of the tooth E@ `and the other side ofthe tooth slot 82. When the tooth passes out of the other end of the tooth slot B2 and the pressure between the work piece and the cutter is released, the rim of the cutter will immediately spring back to its intermediate vposition and the cutter tooth will again align itself with the tooth space as indicated at Stb.

In like manner, upon the reverse stroke the cutter tooth Se will follow the path of the tooth space S3 until such time as the other end of the cutter tooth @Il engages the lower surface of the v blank Si, at which .time there will follow a small lateral displacement to the position indicated at Y. Stic. In this position the cutter tooth Bt is effective to cut the other side 82e of the tooth slot,

`there being clearance between the'side of the toothr and. the side' of the tooth space 82a. This is a very desirable feature in cutting helical gears one which is inherent from the use of a cutter having the characteristics disclosed herein.

Referring now to Figure 5, there is illustrated a method of cutting shoulder gears which employs a cutter of the type disclosed herein. In this case a gear blank 9c on-Which teeth Si are to be formed and which has a shoulder 92 pro-v vided thereon adjacent one end ofthe teeth 9i, is being out by a cutter 93 rockably positioned adjacent an abutment 9d. As will be Aobserved from Figure 5, rocking motion of the cutter 93 into engagement with the abutment 94 tips the cutter blade 95 so that the upper cutting corner 96 is moved into a clearance position with respect to the lower cutting `corner 9T. Upon completion of the stroke, when the lower cutting corner 91 passesr out of the toothed portion 9| of the blank, the flexible web e8 of the cutter will causeV the cutter to assume a neutral position in which the corners e6 and 9T are in alignment with the direction of relative reciprocation and clearance as indicated at e is thus vprovided for the return stroke. It will be observed that in this case cutting takes place only on the down stroke of the cutter assembly and clearance is automatically provided for the return idle upper stroke. This clearance, however, is provided automatically due to the resilience of the thin web 98 and there is no necessrv for backing the cutter assembly out of the tooth slot as' present conventional lpractice.

In the latter case while the cutter portion e has been indicated as having upper and lower cutting' edges se and el it will be appreciated that if desired only the lower surface of the cutting portion 95 need be provided with cutting vedges and that in back of these cutting edges the tooth could be backed on as desired to provide cutting clearance. However, it is preferable t'o provide the tooth with cutting edges at lopposite. ends of each cutting tooth so that the cutter may be re versed as one set of cutting edges becomes dull.

As so :far described, web 6l or d is located midway between the planes of the sides' of the cutter, but in seine cases the web may be nearer one side of the cutter than the other. Thus in Figure 6, web le@ is locatedr nearer to the plane of the top ends of teeth iai than to the plane of the bottoni ends of sai-clteeth.Y This results in dierential radial displacement of the top and bottom ends of said teeth, as suggested by dotted lines ieg and it. Lines 32 and les represent in an exaggerz ated way the position of the teeth during cutting en down `and up strokes respectively. This may result in alternati-ng roughing Vand inishing cuts, or may be particularly useful in cutting shoulder Vgears as described above.

While l have described in considerable detail a speciiic machine, method and cutter assembly tobe used in con-junction with the Shaper cutting or" gears, it will be'appreciated that the invention is of broader scope and is applicable to other types of Shaper cutting such for example as ordinary planing. It will vfurther be appreciated that the present detailed description of my improved -method, machine and tool has been given to ena able those skilled in the art to practice the invention, the scope of which is indicated by the appended claims.

What l claim as my invention is:

1. The method or" shaper cutting helical gears line passing through the teeth in cutting contact which comprises rotating the cutter and a gear blank in timed relation, relatively reciprocating the central portion of the' cutter and gear in cutting relation in a direction parallel to the axis `of the cutter, and displacing the cutting teeth a small distance circumferentially in opposite directions upon cutting strokes in opposite direc'- tichs by tilting the cutting 'teeth about an axis perpendicular to the axis of the 'cutter and to a line joining the centers of the gear blank and cutter 'to cut one side only of the 'gear teeth at one time.

The method oi Shaper cutting helical vgears which comprises relatively reciprocating a gear blank and cutter having an annular cutter portion having helically vformed vcutter teeth vprovided with cutting edges at opposite ends thereof, effecting a slow timed relative rotation between said' blanli vand cutter, superimposing an additional timed rotation between said blank and vcutterto compensate or the relative reciprocation 'and helix angie of 'the teeth,- and providing a relative Yrocking rnotion prior to the initiation of va out in either irection between the cutter l'and blank about an airis perpendicular to the directien oi' relative reciprocation and perpendicular tothe line joining the centers or" cutter and blank and in a direction to provide cutting clearance for the trailing edge oi the cutter teeth, said relative rocking being eiective as a result of rthe helical dispositionoi the cutter teeth to cause cuts to be taken 'alternately bly opposite sides of the cutter teeth. Y

3. The method of -shaper cutting helical gears which comprises relatively reciprocating a gear blank and a cutter having a rigid rib porton having inclined cutting teet i thereon, effectihga relatively slow generating movement between said blank and cutter, superimposing an additional timed movement between said blank and cutter to compensate for thev relative reciprocatioh of cutter and blank and the inclination of the cutting teeth, and providing a relative rocking mtion to said cutting teeth 'prior to the initiation of the cutY in a direction to provide cuttiig'c'le'arance for the trailing edge ofthe cutter teeth, said relative rocking being effective as a result oi the inclination of the cutter teeth to cause cutting by one side vonly of the cutter teeth atone time,

WALTER Si PRAG.Y

eferences Cited ih the ile of 'this' patentv UNITED STATES PATENTS 

